The HST-Hyperion Survey: Companion fraction and overdensity in a z ∼ 2.5 proto-supercluster

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Volume 706 (February 2026)

A&A, 706 (2026) A55

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Table 3.

Relevant merger rates and pair fractions in the literature.

Structure	Type	f_type (%)	M_*/Mag Range	Major?	Redshift Range	Reference
SSA22	Merger	48 ± 10	19.0 ≤R_AB≤ 25.5 mag	No	z ≃ 3.1	1
Field	Merger	31 ± 5	19.0 ≤R_AB≤ 25.5 mag	No	2.5 ≤ z ≤ 3.5	1
SSA22	Merger	38 $_{- 20}^{+ 37}$ $^{+37}_{-20}$	R_AB≤ 25.5 mag	No	z ≃ 3.1	2
Field	Merger	41 $_{- 9}^{+ 11}$ $^{+11}_{-9}$	R_AB≤ 25.5 mag	No	2.9 ≤ z ≤ 3.3	2
BOSS1244	Pair	22 ± 5	log(M_*/M_⊙) > 10.3	Yes	z≃ 2.24	3
BOSS1542	Pair	33 ± 6	log(M_*/M_⊙) > 10.3	Yes	z≃ 2.24	3
Field	Pair	12 ± 2	log(M_*/M_⊙) > 10.3	Yes	2.1 < z< 2.4	3
$\bar{δ} = 0.06$ $\bar{\delta} = 0.06$	Merger	20 ± 0.4	m_UV < 23.5	Yes	z ∼ 2	4
$\bar{δ} = 0.76$ $\bar{\delta} = 0.76$	Merger	20.6 ± 0.9	m_UV < 23.5	Yes	z ∼ 2	4
$\bar{δ} = 0.06$ $\bar{\delta} = 0.06$	Merger	20 ± 1.5	m_UV < 23.5	Yes	z ∼ 3	4
$\bar{δ} = 0.94$ $\bar{\delta} = 0.94$	Merger	24.6 $_{- 2.2}^{+ 2.5}$ $^{+2.5}_{-2.2}$	m_UV < 23.5	Yes	z ∼ 3	4
$\bar{δ} = 0.22$ $\bar{\delta} = 0.22$	Merger	20 ± 0.5	m_UV < 23.5	Yes	z ∼ 4 − 5	4
$\bar{δ} = 2.64$ $\bar{\delta} = 2.64$	Merger	27.7 $_{- 4.4}^{+ 5.2}$ $^{+5.2}_{-4.4}$	m_UV < 23.5	Yes	z ∼ 4 − 5	4
$\bar{δ} = 5.11$ $\bar{\delta} = 5.11$	Merger	35.9 $_{- 10.7}^{+ 14.2}$ $^{+14.2}_{-10.7}$	m_UV < 23.5	Yes	z ∼ 4 − 5	4
Hyperion	CKC	$59_{- 10}^{+ 9}$ $59_{-10}^{+9}$	9.3 ≲log(M_*/M_⊙)	Yes	2.4 < z< 2.7	This Work
Field	CKC	$23_{- 1.8}^{+ 1.7}$ $23_{-1.8}^{+1.7}$	9.3 ≲log(M_*/M_⊙)	Yes	2 < z < 2.4 & 2.7 < z < 3	This Work

Notes. All rates given are derived in similar fashions to our f_ckc metric and are for studies that measure rates for high-z structures at relevant redshift ranges to that of Hyperion (z ≳ 2). Though the assessment techniques and selection methods vary greatly for the limited studies currently available, merger and interaction activity is consistently found to be higher within more overdense regions and/or structures. For the fractions drawn from Shibuya et al. (2025), values are reported for different average levels of galaxy overdensity (δ) rather than at a field versus structure level. Based on our definition of structure (see Section 3.2.2), a δ ≳ 0.62 is the rough threshold we associate with potential structure. (1) Hine et al. (2016); (2) Monson et al. (2021); (3) Liu et al. (2023); (4) Shibuya et al. (2025).

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